SEATTLE (Reuters) - Six underground tanks at the Hanford Nuclear Reservation on the Columbia River in southern Washington state are leaking radioactive waste, but there is no immediate risk to public health, Governor Jay Inslee said on Friday.

Inslee said he was informed of one leaking tank at the decommissioned nuclear weapons plant last week by outgoing U.S. Energy Secretary Steven Chu - but was told by Chu on Friday that radioactive waste was seeping out of a total of six tanks.

"There is no immediate or near-term health risk associated with these newly discovered leaks, which are more than 5 miles from the Columbia River," Inslee said in a statement released by his office. "But nonetheless this is disturbing news for all Washingtonians."

The governor said Chu told him that his department initially missed the other five leaking single-shell tanks because staff there did not adequately analyze data it had.

"This certainly raises serious questions about the integrity of all 149 single-shell tanks with radioactive liquid and sludge at Hanford," he said.

Representatives for the U.S. Department of Energy did not immediately respond to requests for comment on Friday afternoon.

In a press release issued a week ago, the Department of Energy said that declining liquid levels in tank T-111 at Hanford showed it was leaking at a rate of 150 to 300 gallons (568 to 1,136 liters) per year.

The department said in the release that monitoring wells have not identified significant changes in concentrations of chemicals or radionuclides in the soil.

THE MANHATTAN PROJECT

The Department of Energy said T-111 is a 530,000 gallon-capacity underground storage tank that was built between 1943 and 1944 and put into service in 1945. It was classified an "assumed leaker" in 1979 and an interim stabilization project was completed in 1995.

The tank currently holds approximately 447,000 gallons of sludge, a mixture of solids and liquids with a mud-like consistency, the DOE said.

It was not immediately clear if the other five tanks that had been identified as leaking were the same size as T-111 or leaking at a similar rate.

"Secretary Chu has a long-standing personal commitment to the clean-up of Hanford," Inslee said. "He has assured me he will do all he can to address the issue of the leaking tanks. He also assured me there will be immediate additional monitoring of the single-wall tanks."

"The secretary and I agree that the state of Washington and the federal government must have a thorough and candid discussion about the need for additional storage tanks," he said.

The 586-square-mile Hanford Nuclear Reservation was established near the town of Hanford along the Columbia River in 1943 as part of the Manhattan Project, the U.S. government program that developed the first atomic bombs.

According to the U.S. Environmental Protection Agency, production ended at the site in 1989 and work shifted to cleanup of nuclear and chemical waste at Hanford, which is considered one of the largest and most complex such projects in the country.

Weapons production at the site resulted in more than 43 million cubic yards of radioactive waste and 130 million cubic yards of contaminated soil and debris, according to the EPA, which says that approximately 475 billion gallons of contaminated water have been discharged into the soil. (Reporting by Eric Johnson, Steve Gorman and Dan Whitcomb; Writing by Dan Whitcomb; Editing by Paul Thomasch, Cynthia Johnston, Andre Grenon and Lisa Shumaker)